| Recently, in some sewage treatment plants in Japan, seasonal operation is implemented to increase nutrient concentration of treated wastewater in winter as a countermeasure against oligotrophication of sea area where treated wastewater flows in.Seasonal operation aims to improve the quality of Nori (Pyropia) or to increase the production of clam in oligotrophicated sea area, but only a few attempts examined the response of the marine and coastal environment to the increase of nutrient loads of treated wastewater.For example, two treatment plants, Yahagigawa sewage treatment plant and Toyokawa sewage treatment plant, have implemented seasonal operation reducing removal rate of phosphorus since 2016 in Mikawa Bay, a typical enclosed sea area in Japan. In this study, we preliminary examined the effect of seasonal operation on Mikawa Bay costal and estuarine zone, based on the reported data. The relationship between the phosphorus loads from the two treatment plants and the phosphorus and chlorophyll concentration in Mikawa Bay was compared between before and after 2016, when seasonal operation started. |
